1. Field of the Invention
This invention relates to an image forming apparatus and relates specifically to an ink-jet type image forming apparatus and an ink suction pump used therein, in which an image is formed by ejecting ink to a recording medium such as paper.
2. Description of Related Art
Conventionally, an ink-jet type image forming apparatus has, for example, a recording medium transfer member that transfers paper and the like in a specified transfer direction and a recording head carriage arranged opposite a transfer path of the recording medium. The carriage is movable in a direction perpendicular to the transfer direction of the recording medium and ejects ink from the nozzles towards the transfer path of the recording medium.
Moreover, a full color, ink-jet type image apparatus uses a recording head carriage capable of ejecting yellow ink, magenta ink, cyan ink and black ink. Further, the full color, ink-jet type image forming apparatus generally comprises a plurality of recording heads composed of a nozzle component provided for each color, respectively, and an ink tank. Moreover, each of the nozzle components has a plurality of nozzles formed therein and each of the ink tanks is designed to be attachable and detachable from the recording head carriage.
The ink-jet type image forming apparatus carries the recording medium using the recording medium transfer member. A prescribed image is formed on the recording medium by ejecting ink in accordance with image information while the recording medium is being transferred and the recording head carriage is being moved back-and-forth across the transfer path.
However, this type of ink-jet type image forming apparatus has various problems in maintaining image quality. Poor image quality is associated with the ink itself as well as its ejection from the nozzles to form the image.
Specifically, first, the ink dries out in the nozzle components, particularly when no images are being formed. When this condition occurs, the viscosity of the ink increases and, thus, the way the ink ejects from the nozzle components changes so that the desired image is not easily formed.
Second, when foreign material or air enters the nozzles, the ink does not eject properly. Also, when the drying of the ink has progressed, the ink does not eject properly.
Third, it is not possible to properly form the image because of unstable ink ejection caused by the surface of the ink drying directly after beginning image formation.
Fourth, the ink tank may become separated from the recording head and be replaced making it necessary to refill the interior of the nozzle component with ink after replacement.
In the conventional ink-jet type image forming apparatus described above, when images were not properly formed, a plurality of cap members were provided which covered each nozzle component to prevent drying of ink. A plurality of ink suction pumps were also provided for suctioning the ink from each cap member.
However, in the conventional ink-jet type image forming apparatus, it is not possible to miniaturize the apparatus because of the space required in order to have the same number of ink suction pumps as the number of recording heads.
A design for miniaturizing the apparatus was drawn up which reduced space by connecting a plurality of cap members to one ink suction pump. This caused a surplus of space, whereby the area for suction in the one ink suction pump was too large for ink ejection, making the suction operation time consuming because of inefficient suction. This resulted in a waste of ink in the ink suction operation and, in extreme cases, tacky ink became clogged in the nozzle component and could not be suctioned out.
In a conventional apparatus: (1) drying of the ink an be prevented by covering each nozzle with its corresponding cap member; (2) by suctioning the ink when each nozzle is covered by its corresponding cap member, tacky ink or the like can be removed from the nozzles; (3) by ejecting ink from each nozzle directly before image formation begins, ejection blurring of the ink, which occurs at the beginning of image formation, can be prevented. Hereafter, the first will be called the capping action, the second will be called the recovery action, and the third will be called the dummy jet action.
Additionally, among conventional ink-jet type image forming apparatus, there are apparatus that are provided with a recovery cap that can carry out the recovery action as well as cover each nozzle when image formation is not taking place. There are also apparatus provided with storage cap members which only cover each nozzle when image formation is not taking place.
By covering the nozzles with the above-described cap members, drying of the ink can be prevented. By covering the nozzles with the above-described recovery cap member, tacky ink or the like can be removed from the nozzles. Furthermore, by ejecting ink from the nozzles to the recovery cap members directly before image formation begins, ejection blurring that normally occurs at the beginning of image formation can be prevented.
However, in the former conventional image forming apparatus, when tacky ink is removed from a desired nozzle, ink is wasted because ink is suctioned from all the nozzles, not just the desired nozzle. Moreover, the size of the waste ink tank that holds the removed ink must be increased.
Meanwhile, in the latter conventional image forming apparatus, when the dummy jet action is carried out, ink must be ejected from each nozzle in sequence into one recovery cap member. This takes an extremely long time.